INTEROBSERVER AND INTRAOBSERVER VARIATION IN STAGING PATIENTS WITH PROVEN AVASCULAR NECROSIS OF THE HIP

Diagnosis and treatment of avascular necrosis of the hip has long been predicated on the evaluation of plain radiographs, though other modal ities (such as magnetic resonance imaging) are being increasingly used to aid in this evaluation, The Ficat classification is commonly used to assess plain radiographs and to help determine what treatment is ap propriate for a given patient. It also is used to help evaluate patien t outcome after surgical or nonsurgical treatment. This study was desi gned to evaluate the adequacy of plain radiographs in the evaluation o f avascular necrosis of the hip. The plain radiographs of 25 hips with avascular necrosis were analyzed on 3 occasions by 6 readers (450 tot al readings). A clinically significant difference in radiographic stag ing was defined as a Stage I or II reading of the radiographs of a giv en hip on 1 reading and a separate reading of the same radiographs as Stage III or IV. By this definition, interobserver variability for the first reading resulted in clinically significant differences in 10 (4 0%) of the 25 hips. Intraobserver variability resulted in clinically s ignificant differences for 10 (40%) of the 25 hips as well. The most e xperienced readers in the study (a total joint specialist and a muscul oskeletal radiologist) were consistent internally in their readings in 90% of cases, and had a clinically significant difference in only 1 c ase (1%); however, these same 2 readers disagreed with one another on the staging of 9 (36%) of 25 hips, with 4 (16%) of 25 hips having a cl inically significant difference in readings. The kappa statistic for i ntraobserver and interobserver variability was 0.82 +/- 0.16 and 0.56 +/- 0.01, respectively. This high degree of variability suggests that plain radiographs alone are often inadequate for evaluating avascular necrosis of the hip.